Light emitting chip and optical communication apparatus using the same

ABSTRACT

This invention relates to a semiconductor laser of a buried-hetero structure. In this semiconductor laser, the side surfaces of an active layer are in contact with a plane having a stable state of interface. As a result, the threshold current value of this semiconductor laser is low, and a stable operation can be obtained without causing any kink (projection) in the current-optical output characteristics. An optical communication system using this semiconductor layer has a low operating current, and can maintain high coupling efficiency with an optical fiber without the occurrence of noise, so that optical communication having high reliability is possible.

This is a continuation of application Ser. No. 695,004, filed Jan. 25,1985, now U.S. Pat. No. 4,701,927.

BACKGROUND OF THE INVENTION

This invention relates generally to a light emitting chip and to anoptical communication apparatus using the light emitting chip.

The semiconductor laser has been used as a light emitting source inaudio discs, video discs, optical communications, and similar devices.

A buried-hetero structure (hereinafter abbreviated to "BH") has beendeveloped as one of the structures of the semiconductor laser chip ofthe type described above. For example, the magazine "ElectronicsMaterials", published by Industrial Research Association, April, 1979,pages 26-28 describes a GaAs-GaAlAs system BH semiconductor laser, andthe same magazine also describes in the April issue, 1983, page 92, anInP-InGaAsP system BH semiconductor laser. A visible light bandsemiconductor laser (wavelength=0.7-0.9 μm) formed by the GaAs-GaAlAssystem has substantially the same BH laser chip structure as that of along wave band semiconductor laser (wavelength=1.2-1.6 μm) formed by theInP-InGaAsP system.

Now, the long wave band semiconductor laser will be explained by way ofexample.

FIG. 1 illustrates the structure of the BH type semiconductor laserdeveloped by the inventors of the present application prior to thepresent invention. A buffer layer 2 consisting of low concentrationn-type type InP, an active layer 3 (d=0.15 μm) consisting of undopedInGaAsP, a clad layer 4 consisting of p-type InP and a cap layer 5consisting of p-type InGaAsP are sequentially formed by a liquid phaseepitaxial process on an n-type InP single crystal substrate 1 having a(100) crystal plane on its main surface. The total thickness of thesefour epitaxial layers is from approximately 3 to 4 μm. Thereafter, thismulti-layered grown layer is removed by the customary photolithographicprocess with an etching solution such as bromoethanol so that the caplayer 5 is left in a striated form having a width of from 5 to 6 μm.This striated portion is disposed in such a manner as to extend in thedirection of <110> axis of the crystal so that the edge surface of theactive layer 3 becomes a (110) cleavage to improve the light emittingefficiency. In consequence, the crystal exhibits anisotropy with respectto the etching solution described above, and the portion extending overthe active layer 3, the clad layer 4 and the cap layer 5 has an invertedtruncated triangle cross-section, that is, an "inverted mesa" structure.The side plane forming this inverted mesa structure (hereinafterreferred to as the "inverted mesa plane" for the sake of description)becomes a (111) crystal plane on which the In atom appears.

The lower part of the inverted mesa structure of the strip portioncontinues a forward mesa structure described by gentle curves B and C asshown in the drawing, and the boundary between the inverted mesastructure and the forward mesa structure becomes a portion having thesmallest width (hereinafter called a "neck 7" for the sake ofdescription). The portion 6 encircled by a dotted line will be called a"double hetero structure" for the sake of description.

In the drawing, symbol B represents the (111) plane on which the P(phosphorus) atom appears, and symbol C represents the (100) plane orthe plane in the proximity of the former. The active layer 3 is formedabove this neck portion (see "Electronics Materials", published byIndustrial Research Association, April, 1983, page 92, FIG. 7).

After this mesa etching, the portion which has been etched and which hasbecome recessed is buried by laminating a blocking layer 8 covering theside surface of the active layer 3 and consisting of p-type InP, aburied layer 9 consisting of n-type InP and a cap layer 10 consisting ofn-type InGaAsP. Zn is diffused into the mesa portion 9 so as to reachthe intermediate portion of the clad layer 4, and a p+ ftype ohmiccontact layer 11 is defined. Furthermore, electrodes 12 and 13 aredisposed at predetermined positions on the mesa portion and on thereverse of the substrate 1, respectively. The substrate 1 is thendivided in a predetermined manner into laser chips 14 of several hundredμm square. Reference numeral 15 in the drawing represents an insulatingfilm (SiO₂ film).

When used as the light source for optical fiber communication, thesemiconductor layer chip must have characteristics such that it has alow operating current, that a large optical output can be sent into theoptical fiber, that modulation can be made up to a high frequency, thatthe spectral wide is small, and that the change of the opticalcharacteristics with the temperature change is small. The BH laser chiphas been employed so as to satisfy these requirements.

The applicants have made intensive studies in order to develop a laserchip which is operative at a low operating current (low thresholdcurrent I_(th)) and has high performance. The process of these studieswill be described briefly.

First of all, the inventors believe that since the threshold current(I_(th)) of the semiconductor laser depends only upon the width andthickness of the active layer, the position of the active layer at themesa-like double hetero junction is a mere parameter that decides thewidth of the active layer.

Therefore, the inventors have developed a technique which can obtain thewidth of the active layer in a desired width range (e.g. from 1.1 to 1.9μm) with a high yield, and can locate the center position of the activelayer having a thickness of 0.15 μm within a range extending from aposition deviating by 0.5 μm towards the upper side from the neck(hereinafter called the "positive side") to a position deviating by 0.2μm towards the lower side from the neck (hereinafter called the"negative side").

However, in the BH laser chip described above, a problem is encounteredin that, since it is difficult to control the position, (i.e. height)and width, of the active layer 3 and the width of the neck 7, theyreadily tend to deviate from the predetermined values so that thethreshold current (I_(th)) increases while the production yield drops.

The applicants assume that the reason for this is as follows. Since theactive layer is arranged at the position close to the neck having thesmallest width, the width will change drastically if the position of theactive layer moves only slightly upward from the neck.

To cope with this problem, the applicants have produced the BH laserchip by arranging the center position of the active layer 3 above theneck 7 so that the change of the width remains unremarkable even if theposition of the active layer changes in the vertical direction to someextent.

However, many BH laser chips produced in this manner still exhibitgreater threshold current values (I_(th)) than the rated value.

The present invention is completed on the basis of the studies describedabove.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide alight-emitting chip having a low threshold current value.

It is another object of the present invention to provide an opticalcommunication apparatus ensuring stable and highly reliable opticalcommunication by incorporating therein a light-emitting chip having alow driving current and high stability.

The objects of the invention described above can be accomplished by thefollowing construction.

In the light-emitting chip in accordance with the present invention, theside surface of an active layer which emits the laser light from its endsurface is disposed on the (111) plane (B plane) having an interfacestate which is stable and on which phosphorus (P) atoms appear, and thewidth of the active layer is prescribed to 1.6-2.0 μm. Therefore, anunnecessary leakage path does not occur because the side surface of theactive layer is in contact with the (111) plane having a stableinterface state. Therefore, both leakage current and threshold currentvalue can be reduced.

Since the threshold current is small, the driving current also becomessmall, the exothermy of the chip becomes less and laser light emissioncan be effected in a stable manner. Since the occurrence of the kink inthe current-optical output characteristics can be prevented, the laserchip of the invention, when assembled in an optical communicationapparatus, can prevent the occurrence of noise and can stabilize opticalcoupling with an optical fiber, thereby accomplishing opticalcommunication having high reliability.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of the BH laser chip which was developed bythe applicant prior to this invention;

FIG. 2 is a diagram showing the correlation of the threshold currentwith the change of the position of the active layer in the BH laserchip;

FIG. 3 is an equivalent circuit diagram at the double hetero junction ofthe BH laser chip;

FIG. 4 is a diagram showing the V - I characteristics of the BH laserchip;

FIG. 5 is a sectional view of a wafer used for producing the BH laserchip in accordance with the present invention;

FIG. 6 is a sectional view of the wafer after mesa etching in theproduction process of the BH laser chip in accordance with the presentinvention;

FIG. 7 is a sectional view of the wafer after the burying and growingtreatment in accordance with the present invention;

FIG. 8 is a sectional view of the wafer after an ohmic contact layer hasbeen formed in accordance with the present invention;

FIG. 9 is a sectional view of the wafer after electrodes have beenformed in accordance with the present invention;

FIG. 10 is a sectional view of the BH laser chip in accordance with thepresent invention;

FIG. 11 is a sectional view of an oscillator for optical communication(light emitting electronic appliance) which incorporates therein the BHlaser chip in accordance with the present invention;

FIG. 12 is a sectional view of the BH laser chip when a blocking layeris not in contact with a substrate in the present invention; and

FIG. 13 is an enlarged view of principal portions in another embodimentof the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Hereinafter, the present invention will be described with reference to apreferred embodiment thereof.

[Embodiment]

First of all, defect analysis carried out by the inventors of thepresent invention will be described. The inventors have made defectanalysis of the problem described earlier in "Background of theInvention" of this specification, and have found the following fact.

The threshold current I_(th) (hereinafter called also "I_(th) ")exhibits a change such as shown in the diagram of FIG. 2 with therelation between the position of the active layer and that of the neck.When the active layer is positioned on the positive side (or when thecenter position of the active layer 3 is located on the side of the cladlayer 6 (on the upper side) from the neck position), the thresholdcurrent I_(th) increases drastically. In the diagram, the thresholdcurrent I_(th) increases drastically. In the diagram, the thresholdcurrent (I_(th)) [unit: mA] at room temperature is plotted on theordinate and the position (L) of the active layer with respect to theneck (the position of the center portion of the active layer) [unit: μm]is plotted on the abscissa. The dash line represents a line based on atheoretical value when the position of the active layer is nothing but aparameter deciding its width. As shown in the diagram, the thresholdcurrent value I_(th) decreases practically as the active layer ispositioned towards the negative side from the neck (that is, the centerposition of the active layer 3 is on the side of the buffer layer 2 (onthe lower side) from the neck position), and I_(th) attains a minimalvalue of about 24 mA at the position of 31 0.3 μm, and becomesthereafter gradually higher. With the position (L) of the active layerbeing in the range of from -0.6 μm, to -0.7 μm, I_(th) at that positionbecomes substantially equal to I_(th) at L=0, and the I_(th) value isfrom 32 mA to 33 mA. When the position (L) of the active layer becomespositive, I_(th) increases drastically and can not be used any more.FIG. 4 shows the relation between a voltage applied to a laser diode anda current flowing thereby. In the diagram, the dotted line representstheoretical characteristics, but it has been found that the practicalcharacteristics are not in agreement with the theoreticalcharacteristics described above but exhibit those represented by thesolid line.

When the position of the active layer is on the positive side withrespect to the neck as shown in FIG. 3, this difference between thetheoretical characteristics and the practical characteristics isbelieved to result from the existence of a leakpass 17 in parallel withthe laser diode 16.

The difference of the positive and negative positions of the activelayer depends on whether both side surfaces of the active layer ar incontact with the inverted mesa plane (A plane) formed by etching theinverted mesa portion or in contact with the forward mesa plane (Bplane) formed by etching the forward mesa portion. The forward mesaplane (B plane) close to the neck is the (111) plane on which thephosphorus atoms (P atoms) appear, and the inverted mesa plane (A plane)is the (111) plane on which the In atoms appear. It is thereforebelieved that on the (111) plane (B plane) on which P atoms appear,bonding of the interface between the side surface of the active layerand this plane is high, while on the (111) plane (A plane) on which theIn atoms appear, bonding of the interface is not sufficiently high sothat the leak pass occurs.

Two leak passes are believed to occur. The first is a pass through whichthe surface current flows along the (111) plane (A plane) on which theIn atoms appear, from the clad layer 4 to the buffer layer 2. The otheris a pass which occurs because the height of the junction barrier of thep-n junction formed by the block layer 8, which is in contact with the(111) plane (A plane) on which the In atoms appear, and the buffer layer2, is lower than that of the active layer.

The inventors of the present invention have confirmed that lighter atomsother than the In atoms seem to exist on the X-ray photograph of the(111) plane (A plane) on which the In atoms appear. However, it has notbeen clarified yet whether the lighter atoms are contamination that hasbeen deposited on the interface during etching and has remainedunremoved by washing, or foreign matter that has been deposited duringepitaxial growth of the blocking layer, buried layer 9 and cap layer 10.

On the basis of the studies described above, the inventors have realizedthat the threshold current value can be reduced by arranging theposition of the active layer below the neck (on the negative side)because both side surfaces of the active layer 3 come into contact withthe B plane which is the stable plane.

FIGS. 5 through 10 are sectional views showing each respectiveproduction step of the BH laser chip in accordance with one embodimentof the invention. FIG. 11 shows an example when the laser chip isassembled into a box-like package, and is a sectional view of anoscillator for optical communication (light emitting electronicappliance).

First of all, the structure of the laser chip will be describedstep-by-step with reference to the production steps thereof.

Although this embodiment will deal with a BH laser chip of a long bandInP-InGaAsP system by way of example, it is to be understood that thepresent invention can likewise be applied to a BH laser chip of aGaAs-Ga-AlAs system of a visible band. The ratio of each mixed crystalis not described in particular, because it is well known in the art.

The laser chip of this embodiment can be produced in the followingmanner. First, a wafer (semiconductor thin sheet) 18 shown in FIG. 5 isprepared. The wafer 18 consists of 200 μm (d=200 μm) single crystalsubstrate 1 made of n-type InP, having an impurity concentration of5×10¹⁸ atoms·cm⁻³ ; and a multi-layered grown layer which is epitaxiallygrown on the (100) crystal plane of the substrate 1 as its main surface.The multi-layered grown layer consists of a buffer layer 2 (d=1-2 μm)made of n⁻ -type InP, an active layer 3 made of undoped InGaAsP (d 320.15 μm), a clad layer 4 made of p-type InP (d=3.5-4 μm) and a cap layer5 made of p-type InGaAsP (d=0.1-0.2 μm), from the lower layer to theupper in the order named. The active layer 3 has hetero junctions on itsupper and lower surfaces to form a double hetero junction, and is 0.15μm thick.

Next, a plurality of etching masks 19 consisting of about 5 to 6 μm widebelt-like SiO₂ films or the like are formed in parallel with one anotheron the main surface of this wafer 18. The semiconductor layers exposedfrom the masks 19 are etched by an etching solution such asbromoethanol. Etching is made until the surface layer portion of thesubstrate 1 is reached, though the invention is not particularly limitedto this. For example, it may be terminated at an intermediate depth ofthe buffer layer 2. In this case, a laser chip such as shown in FIG. 12can be obtained. The resulting chip is different from the laser chip ofthe first embodiment only in that the etching thickness of the bufferlayer is different, and the buffer layer 2 of the laser chip shown inFIG. 12 is thicker.

Since the masks 19 are disposed so as to extend in the direction of the<>110 axis of the crystal, the portions of the double hetero structureremaining below the masks 19 to extend over the cap layer 5 and the cladlayer 4 has an inverted mesa cross-section. On the other hand, thebuffer layer 2 and the upper layer portion of the substrate 1 have aforward mesa structure which describes a parabola from above to below.The inverted mesa plane becomes the (111) crystal plane (A plane) onwhich the In atoms appear, and the upper end portion of the forward mesaportion becomes the (111) plane (B plane) on which the P atoms appear.The most contracted portion of the double hetero structure 6, that is,the neck 7, is formed at the boundary between the forward mesa portionand the inverted mesa portion. In this embodiment, the neck width isprescribed to be from 0.9 to 1.5 μm, for instance. This means that sincethe inverted mesa plane becomes the (111) plane of the crystal, it canbe formed with high reproducibility by setting in advance the size ofeach layer and the mask width. The active layer 3 which is 0.15 μm thickis formed so that the position of the surface coming into contact withthe buffer layer 2 (that is, the lower surface) is lower (negative) thanthe position of the neck 7. The position of the active layer 3 isbetween 0 and 0.6 μm (at the center position of the active layer) as canbe seen from the diagram of FIG. 2, for example. As a result, the laserchip produced by this method has a low threshold current value (I_(th))ranging from about 24 to 30 mA, and the maximum width of the activelayer 3 is up to 2 μm.

Next, after the masks 19 have been removed from the main surface of thewafer 18, a blocking layer 8 (d=0.5 μm) of p-type InP, a buried layer 9(d=3.5-4 μm) of n-type InP and a cap layer 10 (d=0.1-0.2 μm) of n-typeInGaAsP are sequentially formed by liquid phase epitaxial technique inthe recessed portion formed by etching, as shown in FIG. 7.

Then, a mask 20 is formed on the main surface of the wafer 18 so thatthe upper surface of the mesa portion 6 is exposed, and Zn is thereafterdiffused. The mask 20 may consist of an insulating film such as aCVD-PSG film (phosphosilicate glass film formed by chemical vapordeposition) or a two-layered structure of this insulating film and aphotoresist film used for patterning this insulating film. This Zndiffusion forms a p⁺ -type ohmic contact layer 11 in the mesa portionwhich layer 11 reaches the intermediate depth (0.5-0.8 μm) of the cladlayer 4.

Next, the mask 20 is removed as shown in FIG. 9, and an electrode 12having a lower surface layer consisting of Cr (d=0.7 μm) and an uppersurface layer consisting of Au (d=μm) is formed on the main surface sideof the wafer 18. The portion of the substrate 1 of the wafer 18 isetched. After the substrate 1 becomes about 100 μthick, AuGeNi (d=0.3μm), Pd (d=0.2 μm) and Au (d=1.2 μm) are sequentially evaporated on thereverse of the wafer 18, forming another electrode 13. However, thestate of lamination of these electrodes 12 and 13 is not shown in thedrawing.

Next, the wafer 18 is divided in the desired manner, and a large numberof BH laser chips 14 such as shown in FIG. 10 can be produced.

The present invention is not particularly limited to the embodimentdescribed above, but may have a structure such as shown in FIG. 13. Inother words, since the principal portions of the side surfaces of theactive layer are in contact with the B plane [(111) plane] which is thestable plane, it is possible to prevent the passage of the leakagecurrent.

The laser chip 14 produced according to the steps described above has alight emitting wavelength in the 1.3 μm band, and can be incorporated asa light source in an oscillator 21 for optical communication as shown inFIG. 11. In the oscillator, the laser chip 14 is fixed to a bed 23 atthe center of the recess of a metallic stem 22 (kovar) via a siliconcarbide (SiC) sub-mount 24. A fiber guide 25 made of the kovar isinserted through the peripheral wall of the stem 22 and is hermeticallyfixed to the stem 22 by silver brazing 26. A fiber cable 27 is insertedinto this fiber guide 25. The jacket is peeled off from the inner endportion of the fiber cable 27 to form an optical fiber (diameter=135 μm)consisting of a core (diameter=10 μm) and a clad (diameter=125 μm) insuch an arrangement as to oppose the light emitting surface of the laserchip 14 and to efficiently take the laser light into the optical fiber28. The tip of the optical fiber 28 is held in place by a fixing member29 so that its position relative to the light emitting surface of thelaser chip 14 does not change. The optical fiber 28 and the fiber guide25 are hermetically sealed by silver brazing to prevent moisture fromentering the stem 22 through the optical fiber.

A monitor fiber guide 31 made of kovar is fixed to the other side wallof the stem 22, and a monitor optical fiber 32 at its inner end (havinga diameter of 1 mm) faces the other laser light emitting surface of thelaser chip 14. The monitor fiber guide 31 is fixed to the stem 22 bysilver brazing 33 so as to keep the interior of the stem 22 air-tight.The monitor fiber guide 31 and the monitor optical fiber 32 arehermetically fixed by low melting glass (not shown). The recess of thestem 22 is also maintained air-tight by a metallic cap 35.

When a voltage is applied across the oscillator described above and alead not shown in the drawing, the laser chip 14 emits laser light. Thelaser light is transferred to a desired position through the opticalfiber 28 as the transmission medium. The optical output of the laserlight is constantly monitored by the monitor optical fiber 32 so thatthe optical output becomes constant.

The embodiment of the invention described above provides the followingeffects. (1) In the BH laser chip obtained in accordance with thepresent invention, the position of the active layer is on the negativeside from the neck position of the mesa-like double hetero structureportion, and the side surface of the active layer are out of contactwith the (111) plane having an interface which is believed to beincomplete and on which the In atoms appear. In addition, the width ofthe active layer is as small as from 1.6 to 2 μm. For these reasons, thethreshold current value (I_(th)) becomes as small as from 24 to 30 mA.

(2) Due to the effect described in item (1), transverse mode oscillationbecomes stable, the occurrence of a kink in the current-optical outputcharacteristics can be prevented, and the movement of the near fieldimage and the deflection of the remote field image can be prevented.

(3) Since the position of the active layer is below the neck in thelaser chip of the present invention, it can be easily identified so thatit serves as a guide when discriminating the chips and carrying outintermediate inspection, thus making them easier to produce.

(4) Since I_(th) becomes smaller in the laser chip of the presentinvention, the driving current becomes lower and the exothermy of thechip can be restricted to a low level. Therefore, the temperaturecharacteristics, the optical output and screening yield can be improved.

(5) Since the temperature characteristics can be improved as describedin item (4), the service life of the chips can be extended.

(6) The cost of production of the laser chips having excellentcharacteristics can be reduced due to the effects described in items (1)through (5) described above.

(7) The optical communication apparatus incorporating therein the laserchip of the present invention has a low threshold current value and asmall driving current. Therefore, the occurrence of the kink, themovement of a near field image and the deflection of a remote fieldimage can be prevented so that high optical coupling efficiency can bekept at low power and with less noise, and optical communication can beeffected with a high level of reliability and stability.

It is to be understood that the above-described arrangements are simplyillustrative of the application of the principles of this invention.Numerous other arrangements may be readily devised by those skilled inthe art which embody the principles of the invention and fall within itsspirit and scope.

We claim:
 1. In a light emitting chip comprising:(1) a semiconductorsubstrate of a first conductivity type; (2) a first semiconductor layerof a the first conductivity type coming into contact with a part of saidsemiconductor substrate of the first conductivity type; (3) an activelayer coming into contact with said first semiconductor layer of thefirst conductivity type and having side surfaces; (4) a secondsemiconductor layer of a second conductivity type coming into contactwith said active layer; (5) a third semiconductor layer of the secondconductivity type, coming into contact with a part of said semiconductorsubstrate of the first conductivity type, wherein said thirdsemiconductor layer has an opening which includes a neck portiondefining a point of intersection between an end surface of said thirdsemiconductor layer at said opening and a bottom surface of said thirdsemiconductor layer at said opening, and wherein said thirdsemiconductor layer interposes a part of each of said firstsemiconductor layer of the first conductivity type, said active layerand said second semiconductor layer of the second conductivity type atsaid opening; and (6) a fourth semiconductor layer of the firstconductivity type, coming into contact with said third semiconductorlayer of the second conductivity type, wherein said fourth semiconductorlayer includes an opening and interposes a portion of said secondsemiconductor layer of the second conductivity type at said opening,wherein predetermined portions of said side surfaces of said activelayer are positioned below said neck portion to contact with the 111plane of said third semiconductor layer at said opening of said thirdsemiconductor layer to prevent the flow of leakage current in said lightemitting chip.
 2. The light emitting chip according to claim 1, whereinsaid semiconductor substrate of the first conductivity type, said firstsemiconductor layer of the first conductivity type, said secondsemiconductor layer of the second conductivity type, said thirdsemiconductor layer of the second conductivity type and said fourthsemiconductor layer of the first conductivity type are comprised of anInP compound semiconductor, and wherein said active layer is comprisedof an InGaAsP compound semiconductor.
 3. The light emitting chipaccording to claim 1, wherein said active layer is from 0.1 μm to 0.2 μmthick and from 1.6 μm to 2 μm wide.
 4. In a light emitting chipcomprising:(1) a semiconductor substrate of a first conductivity type;(2) a first semiconductor layer of a the first conductivity type cominginto contact with a part of said semiconductor substrate of the firstconductivity type; (3) an active layer coming into contact with saidfirst semiconductor layer of the first conductivity type and having sidesurfaces; (4) a second semiconductor layer of a second conductivity typecoming into contact with said active layer; (5) a third semiconductorlayer of the second conductivity type, coming into contact with saidfirst semiconductor layer of the first conductivity type, wherein saidthird semiconductor layer has an opening which includes a neck portiondefining a point of intersection between an end surface of said thirdsemiconductor layer at said opening and a bottom surface of said thirdsemiconductor layer at said opening, and wherein said thirdsemiconductor layer interposes a part of each of said active layer andsaid second semiconductor layer of the second conductivity type at saidopening; and (6) a fourth semiconductor layer of the first conductivitytype, coming into contact with said t hird semiconductor layer of thesecond conductivity type, wherein said fourth semiconductor layerincludes an opening and interposes a portion of said secondsemiconductor layer of the second conductivity type at said opening,wherein predetermined portions of said side surfaces of said activelayer are positioned below said neck portion to contact with the 111plane of said third semiconductor layer at said opening of said thirdsemiconductor layer to prevent the flow of leakage current in said lightemitting chip.
 5. The light emitting chip according to claim 4, whereinsaid semiconductor substrate of the first conductivity type, said firstsemiconductor layer of the first conductivity type, said secondsemiconductor layer of the second conductivity type, said thirdsemiconductor layer of the second conductivity type and said fourthsemiconductor layer of the first conductivity type are comprised of anInP compound semiconductor, and wherein said active layer is comprisedof an InGaAsP compound semiconductor.
 6. The light emitting chipaccording to claim 4, wherein said active layer is from 0.1 μm to 0.2 μmthick and from 1.6 μm to 2.0 μm wide.